whine in audio

I have my new audio system installed. looks good (thanks for the input from here) and sounds good at a decent volume. the problem is at low volume or no volume ( as in volume turned all the way down with head unit still on) it has a engine whine noise, how do I get rid of this? Set up, power wire down the middle console, speaker wires on the out side channel by the door.
thanks in advance.

I think I may have found the problem. ( thanks wolfpack for the link) It is the ground on my amp. I grounded to a bolt that is body grounded and not frame grounded if that explanation makes any sense to anyone, moved ground and is all good so far.